P1252: THE ROLE OF PALMITOLEIC ACID IN REGULATING INTESTINAL FLORA TO IMPROVE ACUTE GRAFT-VERSUS-HOST DISEASE AFTER HEMATOPOIETIC STEM CELL TRANSPLANTATION
Authors: Haojie Zhu, Jingjing Xu, Chenjing Ye, Hui Kong, Wenwen Huang, Jianda Hu, Ting Yang
Journal: HemaSphere (2023)

Topic: 21. Stem cell transplantation - Experimental Background: Acute graft-versus-host disease (aGVHD) has limited therapeutic options, and thus restricts the development of allogeneic hematopoietic stem-cell transplantation (allo-HSCT). Recent insights into intestinal homeostasis and uncovering of new pathways have greatly reconciled our understanding of aGVHD pathophysiology. Palmitoleic acid (POA) is a new healthy fatty acid that helps maintain intestinal homeostasis. It has shown tissue repair, anti-inflammatory, antibacterial and immunosuppressive effects when used to treat various diseases, which may be beneficial to mitigate aGVHD. In our previous studies, the cis isomer of POA (cis-POA) was successfully extracted from fish oil and highly purified. Aims: We hypothesized that cis-POA has therapeutic potential on aGVHD by regulating intestinal homeostasis. To verify our hypothesis, this research intends to investigate the anti-aGVHD effect of cis-POA and the underlying microbial, transcriptional, and metabolic pathways participating in intestinal homeostasis. Methods: In this research, we isolated a high-purity POA cis-isomer (cis-POA) from fish oil and developed in vitro and in vivo detection assays for it using high-performance liquid chromatography-tandem mass spectrometry(HPLC/MS), while parameters related to the metabolic kinetics of POA in rats were investigated. With the aid of animal models, we could show the effects of cis-POA in the treatment of aGVHD, including survival, disease regression, target organ repair, and immune tolerance. The mechanism of action of cis-POA was investigated through extensive animal studies and in vitro cellular studies from the reconstruction of intestinal homeostasis including lipid metabolism detected by gas chromatography and mass spectrometry(GC/MS), untargeted metabolome detected by HPLC/MS, microbiome detected by 16s rDNA sequencing, and intestinal transcriptome by RNA sequencing. Results: Cis-POA had the effect of improving outcome, body weight and symptoms in aGVHD mice and was found to have an ameliorating effect on target organ damage by histological examination while the graft-versus-leukemia effect will not be suppressed seen by applying live imaging to examine leukemic mouse models. Flow cytometry showed the ability of cis-POA to inhibit the proliferation of CD8+ T lymphocytes and the expression of CD25 of that in a concentration-dependent manner. In addition, it was found that cis-POA could block inflammatory factor IFN-γ production with a concentration-dependent effect, with no effect on Th2-type factors like IL-4 and no significant inhibition of regulatory factors like TGF-β and Foxp3. We tested the permeability of the intestine of aGVHD mice and its production of butyrate by gavage of FITC-dextran. Cis-POA was found to reduce the permeability of the damaged intestine while increasing the production of butyrate. Application of 16s rDNA sequencing and GC/MS to detect the distribution of intestinal flora and its metabolites in mice revealed that cis-POA might affect intestinal and systemic metabolic profiles through the regulation of intestinal flora, which in turn alters organismal immunity. This immune alteration was mainly manifested in IL-17 and TNF signaling. Summary/Conclusion: We verified the impact of cis-POA on lymphocyte activation and proliferation in vitro and found the beneficial effects of cis-POA in the treatment of aGVHD in mice, of which mechanisms are related to the reconstruction of intestinal homeostasis. This research provides a novel approach for treating aGVHD with promising applications. Keywords: Lipid metabolism, Graft-versus-host disease (GVHD), allo BMT, Mouse model